package com.gylang.easy.lazy;/*


import java.util.NoSuchElementException;
import java.util.Objects;
import java.util.function.Consumer;
import java.util.function.Function;
import java.util.function.Predicate;
import java.util.function.Supplier;

/**
 * A container object which may or may not contain a non-null value.
 * If a value is present, {@code isPresent()} will return {@code true} and
 * {@code get()} will return the value.
 *
 * <p>Additional methods that depend on the presence or absence of a contained
 * value are provided, such as {@link #orElse(java.lang.Object) orElse()}
 * (return a default value if value not present) and
 * {@link #ifPresent(java.util.function.Consumer) ifPresent()} (execute a block
 * of code if the value is present).
 *
 * <p>This is a <a href="../lang/doc-files/ValueBased.html">value-based</a>
 * class; use of identity-sensitive operations (including reference equality
 * ({@code ==}), identity hash code, or synchronization) on instances of
 * {@code Options} may have unpredictable results and should be avoided.
 *
 * @since 1.8
 */

import cn.hutool.core.util.ObjectUtil;

import java.util.NoSuchElementException;
import java.util.Objects;
import java.util.function.Consumer;
import java.util.function.Function;
import java.util.function.Predicate;
import java.util.function.Supplier;

/**
 * @author admin
 */
public final class Options<T> {
	/**
	 * Common instance for {@code empty()}.
	 */
	private static final Options<?> EMPTY = new Options<>();

	/**
	 * If non-null, the value; if null, indicates no value is present
	 */
	private final T value;

	/**
	 * Constructs an empty instance.
	 *
	 * @implNote Generally only one empty instance, {@link Options#EMPTY},
	 * should exist per VM.
	 */
	private Options() {
		this.value = null;
	}

	/**
	 * Returns an empty {@code Options} instance.  No value is present for this
	 * Options.
	 *
	 * @param <T> Type of the non-existent value
	 * @return an empty {@code Options}
	 * @apiNote Though it may be tempting to do so, avoid testing if an object
	 * is empty by comparing with {@code ==} against instances returned by
	 * {@code Option.empty()}. There is no guarantee that it is a singleton.
	 * Instead, use {@link #isPresent()}.
	 */
	public static <T> Options<T> empty() {
		@SuppressWarnings("unchecked")
		Options<T> t = (Options<T>) EMPTY;
		return t;
	}

	/**
	 * Constructs an instance with the value present.
	 *
	 * @param value the non-null value to be present
	 * @throws NullPointerException if value is null
	 */
	private Options(T value) {
		this.value = Objects.requireNonNull(value);
	}

	/**
	 * Returns an {@code Options} with the specified present non-null value.
	 *
	 * @param <T>   the class of the value
	 * @param value the value to be present, which must be non-null
	 * @return an {@code Options} with the value present
	 * @throws NullPointerException if value is null
	 */
	public static <T> Options<T> of(T value) {
		return new Options<>(value);
	}

	/**
	 * Returns an {@code Options} describing the specified value, if non-null,
	 * otherwise returns an empty {@code Options}.
	 *
	 * @param <T>   the class of the value
	 * @param value the possibly-null value to describe
	 * @return an {@code Options} with a present value if the specified value
	 * is non-null, otherwise an empty {@code Options}
	 */
	public static <T> Options<T> ofNullable(T value) {
		return value == null ? empty() : of(value);
	}

	/**
	 * If a value is present in this {@code Options}, returns the value,
	 * otherwise throws {@code NoSuchElementException}.
	 *
	 * @return the non-null value held by this {@code Options}
	 * @throws NoSuchElementException if there is no value present
	 * @see Options#isPresent()
	 */
	public T get() {
		if (value == null) {
			throw new NoSuchElementException("No value present");
		}
		return value;
	}

	/**
	 * Return {@code true} if there is a value present, otherwise {@code false}.
	 *
	 * @return {@code true} if there is a value present, otherwise {@code false}
	 */
	public boolean isPresent() {
		return value != null;
	}

	/**
	 * If a value is present, invoke the specified consumer with the value,
	 * otherwise do nothing.
	 *
	 * @param consumer block to be executed if a value is present
	 * @throws NullPointerException if value is present and {@code consumer} is
	 *                              null
	 */
	public void ifPresent(Consumer<? super T> consumer) {
		if (value != null) {
			consumer.accept(value);
		}
	}

	/**
	 * If a value is present, invoke the specified consumer with the value,
	 * otherwise do nothing.
	 *
	 * @param consumer block to be executed if a value is present
	 * @throws NullPointerException if value is present and {@code consumer} is
	 *                              null
	 */
	public void notEmpty(Consumer<? super T> consumer) {
		if (ObjectUtil.isNotEmpty(value)) {
			consumer.accept(value);
		}
	}

	/**
	 * If a value is present, and the value matches the given predicate,
	 * return an {@code Options} describing the value, otherwise return an
	 * empty {@code Options}.
	 *
	 * @param predicate a predicate to apply to the value, if present
	 * @return an {@code Options} describing the value of this {@code Options}
	 * if a value is present and the value matches the given predicate,
	 * otherwise an empty {@code Options}
	 * @throws NullPointerException if the predicate is null
	 */
	public Options<T> filter(Predicate<? super T> predicate) {
		Objects.requireNonNull(predicate);
		if (!isPresent()) {
			return this;
		} else {
			return predicate.test(value) ? this : empty();
		}
	}

	/**
	 * If a value is present, apply the provided mapping function to it,
	 * and if the result is non-null, return an {@code Options} describing the
	 * result.  Otherwise return an empty {@code Options}.
	 *
	 * @param <U>    The type of the result of the mapping function
	 * @param mapper a mapping function to apply to the value, if present
	 * @return an {@code Options} describing the result of applying a mapping
	 * function to the value of this {@code Options}, if a value is present,
	 * otherwise an empty {@code Options}
	 * @throws NullPointerException if the mapping function is null
	 * @apiNote This method supports post-processing on Options values, without
	 * the need to explicitly check for a return status.  For example, the
	 * following code traverses a stream of file names, selects one that has
	 * not yet been processed, and then opens that file, returning an
	 * {@code Options<FileInputStream>}:
	 *
	 * <pre>{@code
	 *     Options<FileInputStream> fis =
	 *         names.stream().filter(name -> !isProcessedYet(name))
	 *                       .findFirst()
	 *                       .map(name -> new FileInputStream(name));
	 * }</pre>
	 * <p>
	 * Here, {@code findFirst} returns an {@code Options<String>}, and then
	 * {@code map} returns an {@code Options<FileInputStream>} for the desired
	 * file if one exists.
	 */
	public <U> Options<U> map(Function<? super T, ? extends U> mapper) {
		Objects.requireNonNull(mapper);
		if (!isPresent()) {
			return empty();
		} else {
			return Options.ofNullable(mapper.apply(value));
		}
	}

	/**
	 * If a value is present, apply the provided {@code Options}-bearing
	 * mapping function to it, return that result, otherwise return an empty
	 * {@code Options}.  This method is similar to {@link #map(Function)},
	 * but the provided mapper is one whose result is already an {@code Options},
	 * and if invoked, {@code flatMap} does not wrap it with an additional
	 * {@code Options}.
	 *
	 * @param <U>    The type parameter to the {@code Options} returned by
	 * @param mapper a mapping function to apply to the value, if present
	 *               the mapping function
	 * @return the result of applying an {@code Options}-bearing mapping
	 * function to the value of this {@code Options}, if a value is present,
	 * otherwise an empty {@code Options}
	 * @throws NullPointerException if the mapping function is null or returns
	 *                              a null result
	 */
	public <U> Options<U> flatMap(Function<? super T, Options<U>> mapper) {
		Objects.requireNonNull(mapper);
		if (!isPresent()) {
			return empty();
		} else {
			return Objects.requireNonNull(mapper.apply(value));
		}
	}

	/**
	 * Return the value if present, otherwise return {@code other}.
	 *
	 * @param other the value to be returned if there is no value present, may
	 *              be null
	 * @return the value, if present, otherwise {@code other}
	 */
	public T orElse(T other) {
		return value != null ? value : other;
	}

	/**
	 * Return the value if present, otherwise invoke {@code other} and return
	 * the result of that invocation.
	 *
	 * @param other a {@code Supplier} whose result is returned if no value
	 *              is present
	 * @return the value if present otherwise the result of {@code other.get()}
	 * @throws NullPointerException if value is not present and {@code other} is
	 *                              null
	 */
	public T orElseGet(Supplier<? extends T> other) {
		return value != null ? value : other.get();
	}

	/**
	 * Return the contained value, if present, otherwise throw an exception
	 * to be created by the provided supplier.
	 *
	 * @param <X>               Type of the exception to be thrown
	 * @param exceptionSupplier The supplier which will return the exception to
	 *                          be thrown
	 * @return the present value
	 * @throws X                    if there is no value present
	 * @throws NullPointerException if no value is present and
	 *                              {@code exceptionSupplier} is null
	 * @apiNote A method reference to the exception constructor with an empty
	 * argument list can be used as the supplier. For example,
	 * {@code IllegalStateException::new}
	 */
	public <X extends Throwable> T orElseThrow(Supplier<? extends X> exceptionSupplier) throws X {
		if (value != null) {
			return value;
		} else {
			throw exceptionSupplier.get();
		}
	}

	/**
	 * Indicates whether some other object is "equal to" this Options. The
	 * other object is considered equal if:
	 * <ul>
	 * <li>it is also an {@code Options} and;
	 * <li>both instances have no value present or;
	 * <li>the present values are "equal to" each other via {@code equals()}.
	 * </ul>
	 *
	 * @param obj an object to be tested for equality
	 * @return {code true} if the other object is "equal to" this object
	 * otherwise {@code false}
	 */
	@Override
	public boolean equals(Object obj) {
		if (this == obj) {
			return true;
		}

		if (!(obj instanceof Options)) {
			return false;
		}

		Options<?> other = (Options<?>) obj;
		return Objects.equals(value, other.value);
	}

	/**
	 * Returns the hash code value of the present value, if any, or 0 (zero) if
	 * no value is present.
	 *
	 * @return hash code value of the present value or 0 if no value is present
	 */
	@Override
	public int hashCode() {
		return Objects.hashCode(value);
	}

	/**
	 * Returns a non-empty string representation of this Options suitable for
	 * debugging. The exact presentation format is unspecified and may vary
	 * between implementations and versions.
	 *
	 * @return the string representation of this instance
	 * @implSpec If a value is present the result must include its string
	 * representation in the result. Empty and present Optionss must be
	 * unambiguously differentiable.
	 */
	@Override
	public String toString() {
		return value != null
			? String.format("Options[%s]", value)
			: "Options.empty";
	}
}
